An official at ATK Armament Systems said six people were injured. One person had to be taken by air ambulance to a hospital.
A statement from the company said the incident happened in a construction area. A worker at the plant told NBC Action News it was where they load the powder into the bullets.
The company said it could not comment on the extent of the injuries.
The incident is being investigated by the United States Army, ATK safety teams and local authorities.
The entire building was shut down Tuesday night and was to remain closed until at least through Wednesday's day shift, according to a worker at the plant.
ATK Armament Systems is the world's largest manufacturer of military ammunition and integrated medium-caliber gun systems. It is one of four business structures operating under the company name ATK. A second ATK Armament Systems plant in Radford, Virginia produces rocket and gun propellants and other energetics materials.
The Lake City Army Ammunition Plant was built in the 1940s; the plant still produces various rounds for the military. The plant has the capacity to produce 1.4 billion rounds of small-caliber ammunition annually.